Granted Patent
Utility
US 4,491,181 · App. 06/480,877
Method of freeing stuck drill string using spotting fluid
Inventor:
David A. Krol
Patented Case
View Patent ↗
Granted: Jan 1, 1985
Filed: Mar 31, 1983
Inventor
David A. Krol
Assignee (at issue)
Gulf Research & Development Company
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.